U.S. patent number 3,635,531 [Application Number 04/885,469] was granted by the patent office on 1972-01-18 for antiskid device.
This patent grant is currently assigned to Nippondenso Kabushiki Kaisha, Toyota Jidosha Kogyo Kabushiki Kaisha. Invention is credited to Noriyoshi Ando, Hisaji Nakao, Atutoshi Okamoto, Masaharu Sumiyoshi, Koichi Toyama, Hisashi Watanabe.
United States Patent |
3,635,531 |
Okamoto , et al. |
January 18, 1972 |
ANTISKID DEVICE
Abstract
An antiskid device comprising a skid detector composed of a
peripheral wheel deceleration detecting circuit and a peripheral
wheel subdeceleration detecting circuit for differentiating the
output signal from said peripheral wheel deceleration detecting
circuit to detect a first derivative of the peripheral wheel
deceleration (referred to as the subdeceleration hereunder) which
can be regarded to be inversely proportional to the adhesion
coefficient of the road surface, and a braking force controlling
mechanism to control the braking force to be applied to the wheel,
whereby said braking force controlling mechanism is actuated when
the peripheral wheel deceleration from said peripheral deceleration
detecting circuits exceeds a reference value corresponding to the
adhesion coefficient of road, while said reference value is varied
in inverse proportion to the output from said peripheral wheel
subdeceleration detecting circuit to continuously vary the
operation starting point of said braking force controlling
mechanism in accordance with the adhesion coefficient of road such
that said braking force controlling mechanism is operated to
continuously produce the braking force well suited to the adhesion
coefficients of roads ranging from a dry asphalt road surface and
the like where the adhesion coefficient is large to a snowy frozen
road surface and the like where the adhesion coefficient is small,
thereby effecting the antiskidding operation safely and
efficiently.
Inventors: |
Okamoto; Atutoshi
(Toyohashi-shi, JA), Ando; Noriyoshi (Kariya-shi,
JA), Toyama; Koichi (Toyohashi-shi, JA),
Sumiyoshi; Masaharu (Toyota-shi, JA), Nakao;
Hisaji (Toyota-shi, JA), Watanabe; Hisashi
(Toyohashi-shi, JA) |
Assignee: |
Nippondenso Kabushiki Kaisha
(Kariya-shi, Aichi-ken, JA)
Toyota Jidosha Kogyo Kabushiki Kaisha (Toyota-shi,
JA)
|
Family
ID: |
11485579 |
Appl.
No.: |
04/885,469 |
Filed: |
December 16, 1969 |
Foreign Application Priority Data
Current U.S.
Class: |
303/150;
303/115.4; 188/181A |
Current CPC
Class: |
B60T
8/367 (20130101); B60T 8/365 (20130101); B60T
8/4233 (20130101); B60T 8/58 (20130101); B60T
8/4225 (20130101); B60T 8/17633 (20130101) |
Current International
Class: |
B60T
8/58 (20060101); B60T 8/42 (20060101); B60T
8/36 (20060101); B60T 8/1763 (20060101); B60T
8/17 (20060101); B60t 008/12 () |
Field of
Search: |
;188/181 ;303/20,21
;317/5 ;324/160-162 ;340/262-263 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Buchler; Milton
Assistant Examiner: Kunin; Stephen G.
Claims
I claim:
1. An antiskid device comprising:
a skid detector comprising a peripheral wheel deceleration
detecting circuit means for providing an output signal proportional
to wheel deceleration and a peripheral wheel subdeceleration
detecting circuit means for differentiating the output signal from
said peripheral wheel deceleration detecting circuit means to
thereby detect the peripheral wheel subdeceleration as an output
therefrom, and
a braking force controlling means for controlling the braking force
applied to the wheel, wherein said braking force controlling means
is actuated to controllably release the braking force applied to
the wheel when the output from said peripheral wheel deceleration
detecting circuit exceeds a reference value which is varied in
inverse proportion to the output from said peripheral wheel
subdeceleration detecting circuit means.
2. A skid detector for use in a vehicle antiskid device which
device includes brake force control means, said skid detector
comprising:
a wheel deceleration detecting means for producing a deceleration
signal corresponding to the first order time derivative of vehicle
wheel speed,
a wheel subdeceleration detecting means for producing a
subdeceleration signal corresponding to the second order time
derivative of vehicle wheel speed and hence approximately inversely
proportional to the instantaneous coefficient of friction existing
between a road surface and the vehicle wheels
comparing means connected to both of said detecting means and
adapted for connection to said brake force control means for
automatically controlling a release of applied vehicle braking
force when the magnitude of said deceleration signal exceeds a
reference value that is varied in inverse proportion to said
subdeceleration signal.
3. A skid detector as in claim 2 wherein said subdeceleration
detecting means comprises a time differentiating circuit connected
to differentiate said deceleration signal from said deceleration
detecting circuit means.
4. A skid detector as in claim 3 wherein said comparing means
comprises a differential amplifier.
5. A skid detector as in claim 3 wherein said comparing means
includes an inverting amplifier means for inverting said
subdeceleration signal prior to a reference input of said
differential amplifier.
6. A skid detector as in claim 5 wherein said inverting amplifier
means includes a voltage divider means for adjusting the input
signal level to said reference input of said differential
amplifier.
Description
BACKGROUND OF THE INVENTION
This application describes a modification of the apparatus
described in earlier copending commonly assigned application Ser.
No. 832,664 filed June 12, 1969.
FIELD OF THE INVENTION
The present invention relates to antiskid devices adapted for use
with passenger-conveying machines such as automobiles to prevent
the so-called skid wherein the wheels lock under an excessively
applied braking force and thus the vehicle skids with the wheels
locked and to prevent the uncontrollability of the steering wheel
and the spin or irregular gyration of the vehicle and the like due
to such a skid, and more particularly the present invention relates
to an antiskid device wherein the peripheral wheel deceleration
signal and the peripheral wheel subdeceleration signal obtained by
differentiating said deceleration signal are detected to thereby
continuously control the braking force applied to the wheels by
means of said two signals.
With the conventional antiskid devices for automobiles, the
peripheral wheel speed is converted into an electrical quantity by
means of an AC generator connected to a driving axle shaft and then
said AC voltage proportioned to the peripheral wheel speed is
rectified and smoothed out to be converted into a DC voltage. Then,
this DC voltage is applied to a differentiator circuit whose output
signal represents the time rate of change of the DC voltage due to
the drop in the peripheral wheel speed upon the application of the
brakes or the peripheral wheel deceleration which is the time
derivative of the peripheral wheel speed, whereupon when this
peripheral wheel deceleration signal exceeds a reference value
corresponding to a predetermined friction coefficient between the
tires and the road surface which is 0.8, the control is exercised
in a direction to forcibly release the braking force being applied
to the wheels irrespective of whether the driver releases the
brakes applied. Thus, as the peripheral wheel deceleration drops
below said reference value by virtue of said antiskid operation,
the braking force is again applied to the wheels since the brakes
have been continuously applied by the driver. Thereafter, this
process of operation is repeated continuously to prevent the
so-called skid wherein a passenger-conveying vehicle skids with the
wheels being locked.
With the conventional devices described above, if the reference
value for peripheral wheel deceleration is preset to a value
corresponding to the friction coefficient of 0.8 between the road
surface and the tires, for example, to ensure an antiskid operation
which is effective on road surfaces such as a dry asphalt road
where the friction coefficient between the road surface and the
tires is large, even though the brakes are applied urgently on a
dry asphalt road surface or the like where the friction coefficient
between the road surface and the tires has a value close to or
higher than 0.8, the wheels may continue to rotate with a certain
peripheral deceleration by virtue of the aforesaid antiskid
operation until the vehicle is brought to a halt with a result that
the vehicle can be positively braked and stopped without skidding.
However, if the brakes are applied urgently on a snowy frozen road
surface or the like where the friction coefficient between the road
surface and the tires is small, such an 0.1, in spite of the fact
that the antiskid device may not be actuated before the wheels
attain a peripheral deceleration which corresponds to the
predetermined friction coefficient of 0.8, the wheels lock when the
peripheral wheel deceleration is reached which is slightly larger
than one corresponding to the friction coefficient of 0.1, and this
results in the so-called skid wherein the vehicle skids with the
locked wheels as well as the irregular gyration of the vehicle and
the like due to the skid, which are very dangerous. These are the
defects of the conventional devices. In other words, since the
reference value of peripheral wheel deceleration at which the
antiskid device initiates its operation is fixed to a value which
corresponds to the friction coefficient of 0.8 between the road
surface and the tires, these conventional devices have been open to
the objection that a satisfactory antiskid operation cannot be
equally ensured under different conditions, such as in the case of
a dry asphalt road surface and a snowy frozen road surface where
their coefficients of adhesion differ considerably from each other.
Indeed, locked wheels may be avoided even on a snowy frozen road
surface and the like, if the aforesaid reference value is set to a
value which corresponds to the friction coefficient of 0.1 between
the road surface and the tires. However, this gives rise to the
problem of considerably extending the stopping distance required
for the vehicle to come to a stop, and particularly this problem is
so critically manifested on a dry asphalt road surface that the
merit of installing the antiskid device will become null and
void.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide an
antiskid device comprising a skid detector consisting of peripheral
wheel deceleration detecting circuit and a peripheral wheel
subdeceleration detecting circuit adapted to differentiate the
output signal from said peripheral wheel deceleration detecting
circuit to detect a peripheral wheel subdeceleration which may be
regarded as inversely proportional to the adhesion coefficient of
the road, and a braking force controlling mechanism to control the
braking force being applied to the wheels, whereby when the output
from the peripheral wheel deceleration detecting circuit exceeds a
reference value which is controlled inversely proportional to the
output from the peripheral wheel subdeceleration detecting circuit,
that is a reference value controlled to correspond both accurately
and continuously to the adhesion coefficients of road, said braking
force controlling mechanism is actuated to control the braking
force being applied to the wheels in a continuous manner.
According to the present invention, greater effectiveness is
achieved in that not only the uncontrollability of the steering
wheel, irregular gyration of the car body etc., due to the locked
wheels may be avoided even on a snowy frozen road surface and the
like where the adhesion coefficient is small, but also the stopping
distance will never be extended considerably even on a dry asphalt
road surface and the like where the adhesion coefficient is large,
whereby the passenger-conveying vehicles can be always braked and
stopped safely and efficiently in accordance with the adhesion
coefficients of the road and the so-called skid wherein the
passengers conveying vehicles skid with the wheels being stopped
rotating can be completely prevented.
Another remarkable effect of the present invention is the provision
of an antiskid device which is simple in construction and highly
reliable in operation because, excepts its peripheral wheel
deceleration detecting circuit, this device is not provided with
any other converters that convert a physical displacement such as
the peripheral speed of the driving axle shaft etc., into an
electrical quantity.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram showing an embodiment of the antiskid
device according to the present invention.
FIG. 2 is a wiring diagram showing an embodiment of the skid
detector used in the device of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, numeral 1 designates a braking force control
valve interposed in the brake lines of a passenger-conveying
vehicle such as an automobile. Numeral 2 designates an oil pump to
circulate oil under pressure which provides a driving source for
the control valve 1, the oil pump 2 and the oil constituting a
hydraulic pressure source. And a braking force controlling
mechanism is composed of this hydraulic pressure source and the
control valve 1. Numeral 3 designates a cylinder body formed with
axially extended cylinder sections 3 a, 3 b and 3 c. Numeral 4
designates a bell-shaped valve inserted lengthwise and slidably
within the cylinder section 3 a and a hydraulic pressure hole 4 b
is formed through a conical portion 4 a of the valve 4. Numeral 5
designates a spring to urge the valve 4 toward the cylinder section
3 b and it is axially disposed with a chamber A enclosed by the
bell-shaped valve 4 and an end wall 3 d of the cylinder body 3.
Numeral 6 designates a stepped piston-type spool having a small
diameter section 6 a, intermediate diameter section 6 b and large
diameter section 6 c. Thus, the spool 6 is inserted within the
cylinder body 3 such that the small diameter section 6 a and the
cylinder section 3 b define a chamber B therebetween, the
intermediate diameter section 6 b slides within the cylinder
section 3 b and the large diameter section 6 c slides within the
cylinder section 3 c. Numeral 7 designates a spring axially
disposed within a chamber C defined by an end wall 3 e of the
cylinder body 3 and a base 6 d of the large diameter section 6c of
the spool 6, whereby the spool 6 is urged toward the valve 4 by the
spring pressure of the spring so that a base 6e of the small
diameter section 6a of the spool 6 is pressed against and locked by
an expanded base 4 c of the valve 4. Here, it is so designed that
in this pressed and locked position, a chamber D is formed by an
antibase side 6 f of the large diameter section 6 c of the spool 6
and a stepped section 3f formed along the intermediate diameter
section 6b and the large diameter section 6 c. Numeral 8 designates
a manifold having a manifold end 8 a connected to the delivery port
of the oil pump 2, while manifold ends 8 b and 8 c are opened into
the chambers C and D formed in the front and rear of the large
diameter section 6 c of the spool 6. Numeral 9 designates an oil
tank; 10 and 11 nozzles projected into the tank 9 is opposed
relation and separated from each other by a gap, the nozzle 10
being opened into the chamber C through a conduit 12 and the other
nozzle 11 being communicated with the chamber D through a conduit
13. Numeral 14 designates a return conduit adapted to return to the
oil pump 2 the fluid jetted into the tank 9 from the both nozzles
10 and 11 so that the fluid which would otherwise flow away to the
outside of the tank may not do so. Note that the oil forced to
circulate by the oil pump 2 flows in the direction shown by arrows.
Numeral 15 designates a flapper having the top thereof threadedly
secured to a fixed end 16 so that the free end of the flapper is
positioned between the two nozzles 10 and 11 and is swingable
between the nozzles 10 and 11 said flapper top as its supporting
point. Numeral 17 designates a magnetic coil providing a driving
source for the flapper 15 which inclines towards the nozzle 11 as
shown in the figure by a two-dot chain line when the magnetic coil
is energized. Numeral 18 designates a master cylinder which
increases the hydraulic pressure in accordance with the magnitude
of travel of a brake pedal 19. Numeral 20 a designates a hydraulic
pressure feedpipe having one end connected to the hydraulic
pressure delivery port of the master cylinder 18 and the other end
opened into a chamber E formed between the cylinder section 3 a of
the cylinder body 3 and the outer periphery of the conical portion
4 a of the valve 4. Numeral 20 designates a wheel; 21 a tire; 22 a
brake assembly including brakeshoes etc., and mounted on the wheel
20; 23 a wheel cylinder. Numeral 24 designates a hydraulic pressure
feedpipe having one end connected to the hydraulic pressure inlet
port of the wheel cylinder 23 and the other end opened into the
chamber B. A brake system known to the prior art is formed by the
master cylinder 18, brake pedal 19, brake assembly 22, wheel
cylinder 23 etc. Numeral 25 designates a peripheral wheel speed
detecting circuit for producing a DC voltage proportional to the
peripheral wheel speed; 26 a skid detector to detect the presence
of a condition in which the passenger-conveying vehicle is likely
to skid by virtue of operations such as a primary differentiation
and a secondary differentiation of the DC voltage from the
peripheral wheel speed detecting circuit 25.
Now the electrical circuits of the peripheral wheel speed detecting
circuit 25 and the skid detector 26 will be explained in detail
with reference to FIG. 2 in which the peripheral wheel speed
detecting circuit 25 is composed of an AC generator 25 a connected
to a driving axle shaft to produce an AC voltage proportional to
the peripheral wheel speed, a rectifier circuit 25b, smoothing
capacitors 25c and 25 d, and a smoothing resistor 25e. Numerals 26
and 27 designate a resistor and a capacitor respectively which
constitute a primary differentiator circuit, and the time rate of
change of the voltage drop across the smoothing capacitor 25d, that
is, the peripheral wheel deceleration which is the time derivative
of the peripheral wheel speed during the deceleration is taken out
or detected by the primary differentiator circuit such that a
deceleration voltage corresponding to said peripheral wheel
deceleration is developed across the resistor 26. In this case, the
peripheral wheel deceleration detecting circuit is composed of the
peripheral wheel speed detecting circuit 25 and the primary
differentiator circuit. Numerals 28 and 29 designate a resistor and
a capacitor which form a secondary differentiator circuit, and the
time rate of change of the deceleration voltage developed across
the resistor 26 is taken out by this secondary differentiator
circuit, that is, the peripheral wheel deceleration is
differentiated with time to detect the peripheral wheel
subdeceleration which corresponds in inverse portion to the
adhesion coefficient of road such that a peripheral wheel
subdeceleration voltage corresponding to the subdeceleration is
developed across the resistor 28. The peripheral wheel
subdeceleration detecting circuit is constructed by adding the
secondary differentiator circuit to the peripheral wheel
deceleration detecting circuit. Numeral 30 designates a field
effect transistor with a high input impedance for amplifying the
subdeceleration voltage appearing across the resistor 26, and this
field effect transistor 30 may be replace with an emitter follower.
Numeral 31 designates a load resistor of the field effect
transistor 30; 32 a phase inverter transistor to change the phase
of and amplify the amplified subdeceleration voltage developed
across the load resistor 31. Numeral 33 designates a load resistor
of the transistor 32; 34 a resistor which forms a voltage divider
circuit with the load resistor 33. Numerals 35 and 36 designate a
pair of transistors forming a differential amplifier circuit, and
the deceleration voltage developed across the resistor 26 is
applied to the base of the transistor 35 and to the base of the
other transistor 36 is applied the voltage developed across the
junction point A of the resistors 33 and 34 of the voltage divider
circuit, that is, the voltage becomes inversely proportioned to the
subdeceleration or more particularly the voltage which corresponds
to the adhesion coefficient of the road. In this case, the voltage
applied to the base of the transistor 36 represents the reference
value of the peripheral wheel deceleration. Numeral 37 designates a
load resistor of the transistor 35; 38 a transistor which amplifies
the signal voltage appearing across the load resistor 37. Numeral
39 designates a transistor which amplifies the output current of
the transistor 38 to actuate the braking force controlling
mechanism, and the magnetic coil 17 is connected to the collector
of this transistor 39. Numeral 40 designates a storage battery
installed in the vehicle.
Now, with the arrangement described above, the operation of the
device according to the present invention will be described
hereinafter. During a constant speed running with no brakes being
applied or during a normal driving for acceleration, no peripheral
deceleration may develop in the wheel 20, and therefore the voltage
across the junction point B of the resistor 26 and the capacitor 27
for the primary differentiation, which is the output terminal of
the peripheral wheel deceleration detecting circuit for detecting
the peripheral wheel deceleration, that is, the peripheral wheel
speed voltage is either zero or negative and this zero or negative
voltage is applied to the base of the transistor 35 of the
differential amplifier. As a result, the transistor 35 is its
cutoff state. Moreover, when there is no peripheral deceleration
developed in the wheel 20, the voltage across the junction point C
of the resistor 28 and the capacitor 29 for the secondary
differentiation which is the output terminal of the peripheral
wheel subdeceleration detecting circuit, that is, the peripheral
wheel subdeceleration voltage is zero or positive. Therefore, the
field effect transistor 30 to which this zero or positive voltage
is applied has a close-to-conduction level between the drain and
source thereof and its drain voltage has a very low value. Thus,
the transistor 32 is cut off, and the voltage across the junction
point A of the resistors 33 and 34 of the voltage divider circuit
has a value derived by dividing the source voltage with the
resistors 33 and 34. Thus, the transistor 36 to the base of which
is applied the voltage across the junction joint A becomes
conductive. This means that the output voltage of the differential
amplifier composed of this transistor 36 and the transistor 35,
that is, the collector voltage of the transistor 35 has a value
close to that of the source voltage since the transistor 35 is
nonconducting. Consequently, both transistors 38 and 39 are cut off
and no current is supplied to the magnetic coil 17. Thus, the
flapper 15 does not incline toward either of the nozzles 10 and 11,
but it hangs down in the middle of the nozzles 10 and 11.
Therefore, the hydraulic pressures delivered from the oil pump 2
and applied to both sides of the large diameter section 6c of the
spool 6 through the manifold 8 and from the sides of the chambers C
and D are equal to each other and, by the spring pressure of the
spring 7, the spool 6 causes the base 6e of its small diameter
section 6a to be pressed against and locked by the expanded base 4c
of the valve 4. And in this pressed and locked position, the master
cylinder 18 and the wheel cylinder 32 communicate with each other
through the hydraulic pressure feed pipe 20a, the chambers E and B,
and the hydraulic pressure feed pipe 24, whereby normal application
of the brakes can be effected by pressing the brake pedal 19. Of
course, the hydraulic pressure delivered by the oil pump 2 and the
set load of the spring 7 are predetermined so that during normal
brake application, the hydraulic pressure delivered from the master
cylinder 18 will never be applied to the hydraulic pressure
receiving surfaces of the small diameter section 6a and the
intermediate diameter section 6b of the spool 6 to cause the spool
6 to move against the spring pressure of the spring 7.
Now, is the brake pedal 19 is pressed to apply the brakes to cause
the passenger-carrying vehicle running at a high speed to slow down
and run at a low speed or to come to a stop, the peripheral speed
of the wheel 20 rapidly decreases with a certain peripheral
deceleration by virtue of the braking operation of the brake
system. This in turn results in a drop in the output voltage of the
AC generator 25a and a consequent decrease in the voltage across
the smoothing capacitor 25d. Whereupon, the time rate of change of
the voltage across the capacitor 25d or the peripheral wheel
deceleration is detected by means of the primary differentiator
circuit composed of the resistor 26 and the capacitor 27 so that
the peripheral wheel deceleration voltage corresponding to the
thus-detected peripheral wheel deceleration appears across the
resistor 26 with the polarity being positive on the side of the
junction point B and simultaneously this peripheral wheel
deceleration voltage is applied to the base of the transistor 35 of
the differential amplifier circuit. On the other hand, the time
rate of change of the peripheral wheel deceleration voltage
developed across the resistor 26 or the peripheral wheel
subdeceleration is detected by means of the secondary
differentiator circuit composed of the resistor 28 and the
capacitor 29 to thereby indirectly detect the friction coefficient
between the road surface and the tire 21.
The reason why the friction coefficient between the road surface
and the tire 21 can be indirectly detected by detecting the
peripheral wheel subdeceleration will be explained hereinafter. To
begin with, if the wheel 20 is urgently braked on a road surface
such as a snowy frozen road surface where the adhesion coefficient
is small, the peripheral wheel deceleration voltage is developed
across the resistor 26 which is very large in magnitude and very
abrupt, whereas on a road surface such as a dry asphalt road
surface where the adhesion coefficient is large, emergency
application of the brake to the wheel 20 produces across the
resistor 26 the peripheral wheel deceleration voltage of slow and
small magnitude. Accordingly, by differentiating the peripheral
wheel deceleration voltage appearing across the resistor 26 by
means of the secondary differentiator circuit composed of the
resistor 28 and the capacitor 29 to detect the peripheral wheel
subdeceleration, the friction coefficient between the road surface
and the tire 21 can be indirectly detected.
Then, as the peripheral wheel subdeceleration voltage appearing
across the resistor 28 with the polarity being negative on the side
of the junction point C is applied to the gate of the field effect
transistor 30, this field effect transistor 30 proceeds towards its
cutoff state. Consequently, the drain voltage of the transistor 30
rises with a result that base current flows into the transistor 32
in response to this drain voltage and collector current whose
current amplification is .beta. times the base current flows at the
collector of the transistor 32. As a result, the voltage across the
junction point A of the resistor 33 and 34 forming the voltage
divider circuit becomes lower as compared with the voltage
developed during the normal driving without any brake application.
And the, the voltage across the junction point A which is inversely
proportioned to the peripheral wheel subdeceleration or the
reference voltage corresponding to the friction coefficient between
the road surface and the tire 21, is applied to the base of the
other transistor 36 of the differential amplifier.
In this manner, the peripheral wheel deceleration voltage is
applied to the base of the transistor 35 of the differential
amplifier, and the reference voltage inversely proportioned to the
peripheral wheel subdeceleration voltage and corresponding to the
friction coefficient between the road surface and the tire 21 is
applied to the base of the other transistor 36. Thus, when the
peripheral wheel deceleration voltage exceeds the said reference
voltage, the differential amplifier delivers its output to energize
the magnet coil 17 and it is to be noted here that in order to
efficiently brake the passenger-conveying vehicle or to shorten the
stopping distance, it will be an ideal mode of brake application to
provide braking action in a direction to forcibly release part of
the braking force of the brake system just before the wheel 20
locks. Accordingly, the present invention is also based on this
ideal concept and thus, in order to prevent the braking force from
being released considerably until the very moment that the wheel 20
is about to lock, the ohmic values of the resistors 33 and 34 of
the voltage divider circuit are predetermined so that the reference
voltage appearing across the junction point A of the resistors 33
and 34 may be controlled by the voltage-dividing ratio of the
resistors 33 and 34 to thereby prevent the differential amplifier
from delivering its output until about the very moment that the
wheel 20 locks. Then, about the time when the wheel 20 is going to
lock, the peripheral wheel deceleration voltage of very large
magnitude appears across the resistor 26 and the peripheral wheel
subdeceleration voltage of very large magnitude also appears across
the resistor 28 with the polarity being negative on the side of the
junction point C. When this happens, the field effect transistor 30
is completely cutoff and the transistor 32 becomes fully
conductive. This results in a further decrease in the reference
voltage developed across the junction point A of the resistors 33
and 34 of the voltage divider circuit, whereupon, as the peripheral
wheel deceleration exceeds the reference value or the skid detector
detects that the wheel 20 is about to lock, the collector voltage
of the transistor 35 of the differential amplifier is dropped to a
very low level to thereby conduct the transistors 38 and 39.
Consequently, a current which corresponds to the magnitude of the
peripheral wheel deceleration after having exceeded said reference
value, is supplied to the magnet coil 17 causing the flapper 15 to
incline toward the nozzle 11 in response to the current flowing
through the magnet coil 17. This in turn increases the back
pressure of the flapper 15 on the side of the nozzle 11, and the
hydraulic pressure within the chamber D at the rear of the large
diameter section 6c of the spool 6 continuously rises in response
to the peripheral wheel deceleration. This causes the spool 6 to
slide toward the chamber C as shown by a two-dot chain line in FIG.
1 against the spring pressure of the spring 7. Then, the valve 4 is
urged to slide toward the cylinder portion 3b under the spring
pressure of the spring 5 thereby closing the open end of this
cylinder portion 3b. Consequently, the hydraulic pressure path from
the master cylinder 18 to the wheel cylinder 23 is shut off and
simultaneously the movement of the spool 6 causes the volume of the
chamber B to continuously increase in accordance with the magnitude
of the peripheral wheel deceleration. Thus, the hydraulic pressure
in the wheel cylinder 23 continuously drops in response to the
magnitude of travel of the spool 6 so that control is effected in a
direction to release the braking force of the brake system even if
the driver continues to press the brake pedal 19. When the
peripheral wheel deceleration of the wheel 20 gradually decreases
without locking the wheel 20 by virtue of the above braking force
controlling operation and the peripheral wheel deceleration voltage
across the resistor 26 decreases in response to the peripheral
wheel deceleration until it becomes lower than the reference
voltage developed across the junction point A of the resistors 33
and 34 of the voltage divider circuit, the output is no longer
delivered from the differential amplifier circuit blocking the
supply of current to the magnet coil 17. As a result, the flapper
15 now hangs down in the middle of the nozzles 10 and 11, the spool
6 is pressed toward the valve 4 under the spring pressure of the
spring 7, and the base 6e of the small diameter section 6a of the
spool 6 urges the valve 4 toward the end wall 3d of the cylinder
body 3 against the spring force of the spring 5 returning the valve
4 into its normal position with no braking operation taking place.
Thus the master cylinder 18 and the wheel cylinder 23 again
communicates with each other. In this case, since the driver is
still pressing the brake pedal 19, the braking force is applied
again to the wheel 20 developing the peripheral deceleration in the
wheel 20. Thereafter, whenever the peripheral wheel deceleration
exceeds the reference value, the aforesaid antiskid operation is
repeated so that the passenger-conveying vehicle may be safely and
efficiently braked and stopped without the vehicle skidding due to
the locking of the wheel 20.
It is evident from the foregoing that the gist of the present
invention resides in that the reference value (the reference
voltage developed across the junction point A of the resistors 33
and 34 of the voltage divider circuit and applied to the base of
the transistor 36 of the differential amplifier) at which the
antiskid device will be actuated is controlled to be inversely
proportional to the peripheral wheel subdeceleration, whereby the
reference value for controlling the peripheral wheel deceleration
is controlled such that it is set to a small value such as
corresponding to the coefficient of road adhesion, 0.1, on a snowy
frozen road surface and the like where the friction coefficient
between the road surface and the tires is small. While this
reference value for controlling the peripheral wheel deceleration
is set to a large value such as corresponding to the coefficient of
road adhesion, 0.8, on a dry asphalt road surface and the like
where the adhesion coefficiency is large, and thus the reference
value for controlling the peripheral wheel deceleration may be
changed in accordance with the adhesion coefficients of road
surface.
In the embodiment described above, a DC voltage proportional to
peripheral wheel speed is obtained by rectifying and smoothing out
the AC output from the AC generator 25a connected to the driving
axle shaft. However, it is possible to produce a pulse
corresponding to the peripheral wheel speed from a rotary shaft
such as a driving axle shaft correlated with the peripheral wheel
speed by means of a pulse generator and the like and then apply
this pulse to a D-A converting circuit to obtain the DC voltage
proportional to the peripheral wheel speed. It is also possible to
obtain the DC voltage proportional to the peripheral wheel speed by
means of a DC generator coupled to a rotary shaft correlated with
the peripheral wheel speed. Moreover, although the hydraulically
operated braking force controlling mechanism is used in the
illustrated embodiment of the present invention, any electrically
or mechanically operated brake force controlling mechanisms may be
employed likewise.
* * * * *